And as for the propositions, they are divided into definition by genus and species, definition by description, and verbal definition. An example of definition by genus and species is your saying: Man is a rational animal. An example of definition by description is your saying: Man is a writing animal. An example of verbal definition is your saying: Man is Adam, if we assume that the word Adam is more similar and more known than the word man. And all of this third category can be summarized as the interpretation of words translated from one language to another. For example, if we assume that an Arab does not know the meaning of the word Allah, you define it for him verbally by saying to him: Allah is Khoday. And both genus and species definition and description are divided into complete and incomplete, depending on whether it is by the proximate or remote genus, or by the specific attribute, or by the accidental attribute, each of them individually or combined. All of this is clarified in the books of logic. As for syllogism, which is the main purpose of the science of logic, it is that which necessitates another affirmation for its establishment. An example of this is when we say that Allah, the Exalted, must take retribution from the oppressor for the oppressed. Then you say thus: Allah, the Exalted, is a just judge, and whoever is like that, he takes retribution for the oppressed from the oppressor. So the conclusion is thus: Allah, the Exalted, takes retribution for the oppressed from the oppressor. If we accept the first two propositions, we must accept the third proposition. The first two propositions are called premises, one of them is called the minor premise and the other is called the major premise. The spirit of the syllogism is the conclusion. The syllogism is valid if its matter and form are valid, and invalid if either of them is invalid. By the validity of the matter is meant that all its propositions are valid, and by the validity of the form is meant that its structure is such that it produces a conclusion. A valid syllogism is called an argument or proof. As for an invalid syllogism, it is called sophistry, which resembles a valid one but is not valid because its apparent conclusion does not necessarily follow from the valid premises.